Magnetic resonance elastography (MRE) is a phase contrast-based MR imaging technique for observing acoustic strain waves propagating in soft materials (e.g., biological tissues: brain, liver, kidney, muscle, as well as gels, polymers and composites). Mechanical shear waves, typically with amplitudes of less than 100 um and frequencies of 100-500 Hz, are induced using either a piezoelectric or speaker coil oscillator directly coupled to the region of interest. By using multiple phase offsets and motion encoding gradients we acquire data that allows the generation of images that depict shear wave motion and the calculation of local values of the tissue viscoelastic properties. Current MRE studies using 1.5 T MRI systems are directed at establishing techniques for quantifying changes in the mechanical properties of tissues associated with developing disease: malignant tumors appear to be stiffer than benign tumors; fibrosis and cirrhosis tend to increase liver stiffness; and articular cartilage softens in developing osteoarthritis. Work to date suggests that MRE may in fact be able to detect both early stage and diffuse disease well before it can be visualized by conventional MRI, ultrasound or X-ray/CT techniques. Recent MRE investigations are increasingly being conducted at higher spatial resolution to establish histological correlations between elasticity maps and tissue structures; such micro MR elastography (uMRE) studies require stronger static fields, higher performance RF coils and gradients, and more compact, higher frequency mechanical actuators. The goal of the proposed exploratory/development project is to design, develop and validate a new high field (11.74 T) fMRE system (2 cm FOV), 5 kHz maximum acoustic frequency that will provide high spatial resolution (less than 100 fm3 voxel) for the measurement of shear moduli up to 2.5 MPa. These capabilities should allow fMRE to be used to evaluate the microstructure of complex materials, tissues such as articular cartilage and the micromechanical properties of tissue engineered constructs. The specific aims are: 1) Design and build a high resolution fMRE system that operates in the 10 mm diameter clear imaging bore available in an 11.74 T NMR spectrometer (500 MHz for proton); 2) Design, construct and evaluate new mechanical actuators suitable for higher frequency (up to 5 kHz) and multi-frequency shear wave excitation; and 3) Apply fMRE to investigate biological, polymer and composite materials at high spatial resolution.